1. Field of the Invention
The present invention relates to alcohol breath analyzers in general and in particular to a vehicular ignition interlock system comprising an alcohol breath analyzer for enabling the operation of a motor vehicle when the operator thereof has a blood alcohol concentration (BAC) below predetermined threshold level.
2. Description of the Prior Art
A vehicular ignition interlock system for testing the blood alcohol concentration (BAC) of a driver is used for preventing the operation of a motor vehicle by the driver until the driver passes a test demonstrating that his or her BAC is below a predetermined threshold level.
A number of vehicular ignition interlock systems which test for BAC have been proposed. In general, they have required that a person provide a continuous, uninterrupted flow of breath at or above a certain pressure for a predetermined period of time. The pressure and time limitations are intended to insure that the test will comprise a deep lung or alveolar air sample as distinguished from an air sample from the upper portions of the respiratory tract. A deep lung sample which produces gas present in the alveoli of the lungs which has an alcohol content directly proportional to the BAC in the blood stream is required to obtain an accurate measure of BAC. Air samples from the upper portions of the respiratory tract, as is typically provided by short multiple exhalations, are insufficient. Such a system, for example, is disclosed in Collier et al, U.S. Pat. No. 4,093,945.
A disadvantage of the prior known systems described above is that the requirement that a person maintain a continuous, uninterrupted flow of breath at or above a certain pressure for a predetermined period of time in order to pass the test may be difficult for some people to achieve if the required pressure is too high and/or the predetermined period is too long.
Another disadvantage of the prior known systems as described above is that they can be defeated by using a bogus air source such as a pre-filled balloon, air pump or the like for providing the air sample.
Various means have been employed to prevent the use of a bogus air source. For example, in Collier et al, U.S. Pat. No. 4,738,333, there is disclosed a system for confirming the identity of the operator which requires the operator to perform a pre-learned identity-confirming physical act. The act may comprise, for example, any one of a number of breathing sequences, difficult to duplicate in a short time, comprising periods of blowing and non-blowing. In Elfman et al, U.S. Pat. No. 4,678,057, there is disclosed a system which requires the acquiring and storing of a reference breath signature which is compared against a breath sample which is taken during testing.
While possibly necessary for preventing a sober person from taking the test for an inebriated person, the above-described apparatus and methods are seen as being too complex, expensive and difficult to use if what is desired is to simply prevent an inebriated person from using a pre-filled balloon, air pump or the like as a source of an air sample in order to defeat the system.